1. Field of the Disclosure
The present disclosure relates to an accelerator-pedal reaction force control apparatus which controls a reaction force of an accelerator pedal of a vehicle.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2003-120339 (hereinafter referred to as Patent Document 1) discloses a technique for increasing a reaction force against depression (hereinafter also referred to simply as reaction force) of an accelerator pedal. This technique is applied to an engine which switches between a first operation method (for example, homogeneous combustion) for a high-rotational-speed, high-load operation and a second operation method (for example, stratified combustion) for a low-rotational-speed, low-load operation in which fuel efficiency is higher than that in the first operation method. According to this technique, in a process of switching an engine operation from a second operating range in which the second operation method is used to a first operating range in which the first operation method is used, the reaction force is suddenly increased at the time when the engine operation enters a boundary operating range immediately before entering the first operating range. The amount of increase in the reaction force is eliminated when the engine operation returns to the second operating range from the boundary operating range.
According to the technique of Patent Document 1, the reaction force of the accelerator pedal is increased or the amount of increase therein is eliminated in the boundary operating range for the purpose of reducing the specific fuel consumption. However, the accelerator pedal is a main operating member operated by the driver to drive the vehicle in a way that the driver desires. Therefore, the operational feel of the accelerator pedal and the influence thereof on the vehicle driving performance directly affect the overall quality evaluation made by the driver. For this reason, this type of reaction-force control apparatus which contributes to the reduction in fuel consumption cannot be put into practical use unless the reduction in fuel consumption can be achieved together with satisfactory operational feel of the accelerator pedal and operability of the vehicle.
Various tests have been performed for putting the reaction-force control apparatus which contributes to the reduction in fuel consumption into practical use. As a result of these tests, it was found that if the reaction force is increased or the increase therein is eliminated at a certain accelerator opening degree which corresponds to a boundary as described in Patent Document 1, unfavorable operational behavior finally occurs as a result of an unintentional response by a driver.
More specifically, according to the technique described in Patent Document 1, when the driver depresses the accelerator pedal and the operating range is changed from the second operating range to the boundary operating range, the reaction force suddenly increases. Therefore, there is a possibility that the accelerator pedal will be pushed back against the intention of the driver and the operating range will return to the second operating range from the boundary operating range. In such a case, the reaction force, which has been suddenly increased when the operating range has been changed from the second operating range to the boundary operating range, will be suddenly reduced. Since the original intention of the driver was to depress the accelerator pedal and the depression of the accelerator pedal caused the increase in the reaction force, the driver tends to depress the accelerator pedal again when the operating range is changed from the boundary operating range and the reaction force is reduced. As a result, the operating range changes from the second operating range to the boundary operating range again, and the reaction force suddenly increases accordingly. Consequently, the accelerator pedal will once again be pushed back against the intention of the driver.
Thus, when the driver increases the accelerator opening degree such that the fuel efficiency of the vehicle changes beyond a certain boundary, there is a risk that the accelerator pedal will unstably move up and down against the intention of the driver. This makes the user feel uncomfortable and degrades the operability of the vehicle.